Methods are well-known for fusing bundles of optical fibers. The methods involved fusing individual fibers (e.g, U.S. Pat. No. 3,626,040 and U.S. Pat. No. 5,045,100) or preform blocks of fibers (multi or multi-multi-fiber bundles) (U.S. Pat. No. 4,175,940) using conventional methods under well-known conditions and techniques. Such methods have been applied to a wide variety of optical fiber glass types (or polymer (U.S. Pat. No. 4,758,064)), sizes, and applications. Fusing techniques are also utilized for formation of other fiber optic structures such as couplers (U.S. Pat. No. 5,066,087). U.S. Pat. No. 3,204,326 also discloses fusing processes using rolling mill equipment where fused bundles of a variety of cross-sectional shapes are produced from unfused original assemblies of a variety of shapes.
It is also known to draw out such fused fiber optic bundles by conventional pulling or drawing processes. These methods are utilized simply to decrease the overall dimension of a given fiber optic bundle or to prepare tapered optical fibers (U.S. Pat. Nos. 4,115,940, 3,190,735 and 4,076,978) having ends of proportionately decreased dimensions.
A typical application of such drawn tapered fiber optic bundles is for coupling imaging devices having disproportionate formats, e.g., different sized rectangles at each end, a rectangle at one end and at square at the other end, a circle at one end and a square at the other end, etc. In conventional practice, a fiber optic bundle best accommodating the larger imaging device is tapered such that its other end accommodates to the extent possible the smaller imaging device. These conventional tapers are produced by the drawing processes and simply proportionately reduce at the smaller end the center-to-center fiber spacing at the original larger end. Thus, the size modifications along each of the X and Y axes at each end of the tapered fiber bundle are equivalent. Coupling of the two disproportionate imaging devices by such a conventional tapered bundle is accomplished by over- and/or under-filling each of the formats, thereby leaving ineffective either some fiber optic pixels or some border area of the imaging device. This reduces both the number of active pixels and system resolution.
In certain situations, pressing techniques have also been applied to fiber optic bundles. Typically, these techniques are employed to fuse the bundles, as discussed in the references above, e.g., U.S. Pat. No. 3,626,040. Emphasis is placed on uniform application of pressure in order to avoid non-uniformities, especially distortions of the fibers in the bundles, especially the outer fibers (See, e.g., U.S. Pat. No. 4,175,940.)
Pressing techniques have not heretofore been applied to the production of tapers because of the serious tendency toward introducing distortions in the outer fibers caused by effects of heat or non-uniform pressing imposed, e.g., by contact between the pressing device and the fiber bundle. Such defects were noted in the conventional uniform pressing operations used to fuse fibers; heretofore, the problems were expected to be greatly exacerbated were a taper to have been attempted where the shape of the fiber at each end of the taper is to be different and/or the ratio of the fiber dimensions along the X and Y axes is to be changed disproportionately (the Z axis being the longitudinal axis of the fiber).
Consequently, there remains a need for a tapered anamorphic fused fiber optic bundle where the shape at one end is configured to fit precisely the corresponding cross-sectional shape of an imaging device and the shape at the other end is configured to fit precisely the cross-sectional surface area of a second imaging device to be coupled to the first, and wherein the cross-sectional dimensions at one end are anamorphic with respect to the other.